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Control Strategy And Closed-loop Parameters Design Of Synchronverter

Posted on:2016-03-17Degree:MasterType:Thesis
Country:ChinaCandidate:X K LiFull Text:PDF
GTID:2322330479452925Subject:Electrical engineering
Abstract/Summary:PDF Full Text Request
Renewable energy based distributed power generation system(RE-DPGS) is one of the most effective way to develop and utilize renewable energy, which is beneficial to alleviation of energy crisis and environmental pollution. Grid-connected inverter is the interface between the RE-DPGS and the power grid. Synchronverter is the grid-connected inverter that mimics a synchronous generator to provide grid support by automatically changing its active and reactive power based on the frequency and amplitude of grid voltage. This thesis is dedicated to the control and closed-loop design of the synchronverter.The mathematical model of synchronous generator is derived in detail in this thesis, and then the control method of synchronverter is introduced from the perspective of mimicing the synchronous generator, including the synchronous generator's inertia, frequency-active power droop characteristics and voltage amplitude-reactive power droop characteristics.In order to illustrate the function of synchronverter's virtual inertia, this thesis Compares the virtual inertia control and the droop control. It is concluded that the virtual inertia can improve the stability of the system frequency and amplitude of the output voltage. Then propose the line-frequency-averaged small-signal model of its power loops of the synchronverters is derived, and it is pointed out that the coupling effects between the active power loop and the reactive power loop can be ignored. As a result, the control parameters of each loop can be designed independently. A design method of the control parameters is proposed based on the system cut-off frequency and phase margin requirements. This design method has the advantage that the control parameters can be easily determined taking into account that the stability, the dynamic performance and the attenuation of pulsating power of the system.The influence of the dead time of the power switches in the synchronverters on the output voltage and the injected grid currents is analyzed, and it is pointed out that the unmatched dead time of the two power switches in a bridge leg will result in dc component in the injected grid currents. A method of virtual capacitor is proposed to eliminate the dc component of the injected grid currents.A 20 kW synchronverter prototype has been built and tested in the lab, and the experimental results are given to verify the effectiveness of the synchronverter's control strategy and the theoretical analysis.
Keywords/Search Tags:Synchronverter, Grid-connected inverter, Virtual inertia, Small-signal model, Virtual capacitor
PDF Full Text Request
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